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Full text of "Text Book Of Mechanical Engineering"

692

Compound Locomotive.

blast pipe 39, gradually contracted towards the orifice to cause the
necessary velocity ; and the smoke box 22 must be air tight, so its
door 33 is provided with two handles, one for turning the tongue
catch, and the other for tightening the screw. A jet of steam
from the blower 40 causes draught when the engine is standing.
The steam regulator, 56, has two slide valves worked from, handle
34, the main valve 27 being treble-ported, and the 'easing' valve
28 double-ported and small. A pin 55 connects both valves to
the gear; but the hole in 27 is slotted, so that when opening, 28
is first moved (easily, being small) and a film of steam admitted
'between the main valve and its seat. Next, 27 is caught by the
pin, and, on account of the relief just given, can be moved
without difficulty.

Under ordinary conditions steam first enters the H. P. cylinder
B by the pipe 27, exhausts thence to the L. P. cylinder through
30 and 28 (the whole pipe forming a receiver of a capacity equal
to B), and finally leaves by the blast pipe 39. But if H. P. crank
be on a dead centre at starting, steam must first be admitted to
the L. P. cylinder A, and yet be prevented from entering B for
fear of blocking the piston. Outside the smoke box a valve box
61 is fixed, having a starting valve 59 opened by a rod from the
foot plate when required, but at other times kept closed by a
strong spring. Pipe 41 takes steam from the boiler to 61, and 57
carries it away to the main pipe 28, entering at 29; and a piston
62, fitting in the valve box 61, is connected to the rod 60 for the
purpose of lifting the flap or intercepting valve 58, which is
normally open. When the driver wishes to start, he opens
regulator valve 27, and if the H. P. piston refuses to move, he
pulls the small lever which opens 59; and steam, wire-drawn to
half pressure, enters 61, moves 62 clear to the left and closes 58,
then passes by 57 and 29 to move the L. P. piston. Once the
engine moves, steam enters the H.P. cylinder by 27, the proper
path, exhausts by 30 and 29, and acting on the large area of the
flap 58, opens it, and once more valve 59 is closed by its spring.

Instead of feed pumps, injectors are now favoured for feeding
locomotive boilers, and two of these, 12, 12, are supplied. They
draw from the tender through a strong rubber,pipe, and deliver
through the clack box 25, in which is a non-return valve. A